1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and an image processing program which eliminate the influence of noise in a background area in an image of a document or a sheet by extracting an area including pixels that are colored by the entry of predetermined information such as a character into the document or the sheet.
2. Description of the Related Art
Various methods have been proposed as a method of eliminating noise from a gray-scale image of a document. One of conventional noise eliminating arts smoothes a gray-scale image by an averaging filter or a Gaussian filter (see, for example, Non-patent Document 1, pp. 108-110).
Further, one of methods described in the non-patent document 1 performs a morphology operation such as opening on a binary image (the same document pp. 179-180).
Non-patent Document 1 also discloses, as a method of generating a binary image with less noise influence, a method of eliminating isolated points from the binary image by a median filter or the like (the same document p. 113).
However, in a case where density distribution in a background portion is wide and largely overlapped with density distribution of black pixels caused by entry, if an area where the density of background pixels happens to be high is too large to be recognized as an isolated point, these methods cannot eliminate this area as noise.
[Non-patent Document 1] Digital Image Processing, Computer Graphic Arts Society (CG-ARTS Society), Jul., 2004, pp. 108-113, pp. 179-180